NL8001878A - PROCESS FOR THE PREPARATION OF ALDEHYDES. - Google Patents

Description

1.

STAMICARBON B.V.

Inventors: Theodorus F.M. DE GRAAF in Beek (L)

Hubertus J.A. DELAHAYE te Voeréndaal 1 3173 __ METHOD FOR PREPARING ALDEHYDES ________ ^ _________

The invention relates to a process for the preparation of aldehydes by dehydrogenation of monovalent primary alcohols.

British Patent 1,444,484 discloses a process for dehydrogenating alcohols in the gas phase using a copper-containing catalyst in which, to obtain a long operating time of the catalyst, very good selectivity and high conversion dehydrogenation is carried out in the presence of. water vapor and small amounts of an indifferent gas.

The use of water vapor in such dehydrogenation has the consequence that during the development of the resulting gaseous reaction mixture, by condensing it and separating the condensate by% distillation, problems often arise due to azeotrope formation of the reaction product to be recovered and any present starting product with water.

It is true that such an azeotropic mixture can be recirculated, but in many cases this means a large recirculation of the desired product.

When using the process according to said British patent for the dehydrogenation of monovalent primary alcohols, the life of the catalyst and the selectivity of the conversion to aldehyde is also less satisfactory.

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A process has now been found for the dehydrogenation of monovalent primary alcohols in which no water vapor needs to be added to the starting product and a very long catalyst life as well as high selectivity can be achieved.

The process according to the invention for the preparation of aldehydes by dehydrogenation of monovalent primary alcohols in the gas phase by means of a copper-containing catalyst is characterized in that the dehydrogenation is first carried out in the presence of an indifferent gas and then the catalyst used therein. used to carry out the dehydrogenation in the presence of a mixture of an indifferent gas and hydrogen.

In the process according to the invention, various monohydric primary alcohols can be used as starting products, in particular monovalent primary alcohols with 2-20 carbon atoms, such as, for example, ethanol, octanol-1, decanol-1, dodecanol-1,2 -hexenol-1, undec-10-enol-1,2 methyl undecanol-1, phenylethanol and cinnamon alcohol.

Nitrogen is preferably used as indifferent gas, but other indifferent gases can in principle also be used. The amount of indifferent gas C separately and in the mixture with hydrogen) can vary within wide limits, for example 2-100 moles of indifferent gas per mole of alcohol originally present. A very suitable result can be achieved by using 5-40 moles of indifferent gas per mole of alcohol originally present.

The amount of hydrogen can also vary within wide limits, for example 0.5-50 moles of hydrogen per mole of alcohol originally present. Preferably 1-20 moles of hydrogen per mole of alcohol originally present are used.

The dehydrogenation period of the invention using only indifferent gas is terminated when the catalyst has reached the desired level of selectivity, which can generally be accomplished in a time of 2-24 hours. Thereafter, by using the mixture of indifferent gas and hydrogen, the desired level of selectivity of the catalyst can be maintained for a long time, for example several months.

In the process according to the invention, per se known copper-containing dehydrogenation catalysts can be used, such as copper with as support, for example magnesium oxide, zinc oxide, chromium oxide, aluminum oxide, silicon oxide or a mixture of two or more of the above oxides. If desired, oxides of alkali and / or alkaline earth metals can be added to the catalyst as a promoter.

In general, temperatures of 200-450 ° C are suitable for carrying out the dehydrogenation according to the invention.

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A temperature of 225-350 ° C is preferably used. By increasing the temperature very gradually within the desired limits, for instance a temperature increase corresponding to an average of one degree Celsius per three days, the activity of the catalyst can be kept constant for a long time.

For example, the spatial flow rate during dehydrogenation is chosen between 0.05 and 10 kg of alcohol per liter of catalyst (bulk volume). A lower or higher spatial throughput »800 1 8 78 3

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can in principle be applied, but this does not result in any advantage.

The gaseous reaction mixture obtained in the process according to the invention can be separated by cooling into a condensate containing the desired product and a gas mixture which can be recycled if desired. If this gas mixture is recycled, however, given the formation of hydrogen in the dehydrogenation, the amount of hydrogen formed must be removed. The condensate obtained in said cooling can be separated by distillation into the aldehyde formed and any unreacted alcohol which can be reused.

The aldehydes obtained in the process according to the invention can be used as raw material for the preparation of various valuable products such as, for example, fragrances.

The following examples further illustrate the invention.

Example I

Through a vertical glass tubular reactor (internal diameter 25 mm, height 40 cm), filled with 25 ml catalyst granules (Cu on MgO, 45 wt.% Cu, diameter and length of the granules, respectively 3 and 5 mm) for 10 an hourly gaseous mixture of okanol-1 (16.5 g per hour) and nitrogen (20 mol per mol octanol) from top to bottom at atmospheric pressure over the catalyst. Using a jacket heating, the temperature in the reactor (measured at about 1 mm above the catalyst) is kept at about 265 ° C. Subsequently, during a period of 4 weeks, with a very gradual increase in temperature (at the end of said period, the temperature is 329 ° C), a gaseous mixture of hydrogen, nitrogen and octanol-1 (16.5 g of octanol per hour, 1 mole of hydrogen and 9 moles of nitrogen per mole of octanol) were passed over the catalyst and the resulting gaseous reaction mixture was discharged through a collecting vessel cooled to 12 ° C. The condensate thus formed in the receiving vessel is periodically analyzed by gas chromatography. From this analysis it appears that the selectivity, 4 days after the transfer of the hydrogen-containing gas mixture has started, is 99% and the conversion of the octanol 58%. During the further course of the experiment, the selectivity and the conversion remain respectively.

35 99 and 58%.

The catalyst used in this example is prepared in known manner by co-preparation from a copper and magnesium salt containing solution followed by filtration drying, granulation and reduction of the granules in the reactor. For this reduction, the o granules in the reactor are heated to 265 ° C while passing through 60 l of nitrogen and 0.5 l of hydrogen per hour, after which the granules are kept at 265 ° C for 16 hours while passing through 60 l of nitrogen and 2 1 hydrogen per hour (stated amounts of nitrogen and hydrogen are expressed in liters of 0 C and 100 kPa).

Example 11 Example 1 is repeated, however, using a different mole ratio of hydrogen: nitrogen: octanol, namely 2.5: 7.5: 1.

The selectivity is 99% and the conversion 45% after 4 days after the transfer of the hydrogen-containing gas mixture has started. The experiment is terminated after 12 weeks (at the end of this period 15 the temperature is 313 ° C) without a decrease in selectivity and conversion.

Example III

Example II is repeated, however, using an o temperature of 275 ° C (instead of the temperature of 265 ° C as stated in Example I). The experiment is terminated after 6 weeks (at the end of this period the temperature is 317 ° C). The selectivity is 99% and the conversion 55%.

Comparative example A

Example II is repeated, however, without the initial period (as described in Example I) during which the octanol-nitrogen mixture is passed over for 10 hours. During a 6 week experiment (at the end of this period the temperature is 290 ° C) the selectivity is only 30%. The conversion is 75%. This low selectivity is unacceptable in practice.

Comparative example B

Example I is repeated. Instead of 1 mol hydrogen and 9 mol nitrogen, 10 mol nitrogen per mol octanol is now used.

The conversion now appears to be falling rapidly.1. about 10% per day (because of an increase in temperature, this decrease cannot be prevented, while maintaining sufficient selectivity), so that the experiment ends after a few days.

Comparative example C _._________ ___________. 5. . . . Example I is repeated. Instead of 1 mole of hydrogen .....

. . and 9 moles of nitrogen now use 5 moles of hydrogen per mole of octanol.

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Instead of a temperature of 265 ° C as in Example 1, a temperature of 305 ° C is used to achieve a good conversion (50%). Maintenance of a good conversion with sufficient selectivity appears to be possible only for a short time (a few days).

Example IV

Example I is repeated with decanol-1. First a nitrogen-decanol mixture (20 moles nitrogen per mole decanol, 16.6 g decanol per hour) is passed over the catalyst for 10 hours and then also hydrogen (2.5 moles hydrogen and 7.5 moles nitrogen per mole) decanol).

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The receptacle is cooled to 30 ° C. After the hydrogen-nitrogen-decanol mixture has been passed for about 4 days, a selectivity of 99% is achieved, at a conversion of 40%, which values are maintained during the 6-week experiment (the temperature 20 at the end of the experiment is 289 ° C).

Example V

Example IV is repeated, however, using an o temperature of 275 ° C (instead of the temperature of 265 ° C as set forth in Example I). After the hydrogen-containing mixture has been passed for about 4 days, the selectivity is 99% and the conversion 50%, which values are retained during the 6-week experiment (temperature at the end of the experiment 317 ° C).

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Claims (7)

1. Process for the preparation of aldehydes by dehydrogenation of monovalent primary alcohols in the gas phase by means of a copper-containing catalyst, characterized in that the dehydrogenation is first carried out in the presence of an indifferent gas and subsequently according to the used catalyst to carry out the dehydrogenation in the presence of an indifferent gas and of hydrogen. 2. Process according to claim 1, characterized in that 5-40 moles of indifferent gas are used per mole of alcohol originally present. Process according to claim 1 or 2, characterized in that 1-20 moles of hydrogen are used per mole of alcohol originally present. 4; Process according to any one of claims 1-3, characterized in that the dehydrogenation is carried out at a temperature of 225-350 ° C. 5. Process according to any one of claims 1-4, characterized in that the temperature is gradually increased during dehydrogenation in the presence of the indifferent gas and of hydrogen. A method according to claim 1, as substantially described and further elucidated in the examples. _ 6 3173 CON CL PS IES 7. Aldehydes obtained using the method according to any one of the preceding claims. RAP / JB 800 1 8 78